Inductive repulsion type magnetically levitated railways in general are known.
An example of a levitation-propulsion-guidance mechanism for such a railway is shown in FIGS. 1-4. Superconducting coils 2 and 2' are vertically mounted on both sides of the truck 1 of the vehicle V. Conductor coils 3 and 3' for levitation of the vehicle are constituted by conductor-loop coils or conductor-sheets arranged horizontally on the bottom surface of the track 5 having a U-shaped section, and they extend continuously in the direction the vehicle travels on the track 5. The arrangement is as illustrated in FIGS. 2(a)-2(e). Vertically positioned conductor coils 4 and 4' for both guidance and propulsion of the vehicle extend continuously along both sides of the track in the direction of travel of the vehicle at intervals such that they can magnetically couple with said conductor coils 2 and 2' installed on the truck 1.
The vehicle V is levitated by means of said conductor coils 3 and 3' and said superconducting coils 2 and 2' and is propelled and guided by means of said conductor coils 4 and 4' and said superconducting coils 2 and 2'.
The above relationship is shown in detail in FIGS. 2(a)-4.
FIG. 2(a) shows schematically the known superconducting coils 2 and 2' of loop form which are vertically mounted at definite intervals on both sides of the truck 1 in the direction of travel of the train. Usually the adjacent superconducting coils possess mutually opposite polarities.
On the other hand, at the bottom of the track are the conductors 3 and 3' consisting of conductor-loop coils or conductor-sheets which are arranged continuously and which extend horizontally in the direction of travel of the vehicle with gaps such that magnetic induction can take place between the conductor coils 2 and 2' and said conductors 3 and 3'.
Even with this arrangement of these conductors, however, there will never be any magnetic interaction between said superconducting coils 2 and 2' on the vehicle and the conductor coils 3 and 3' on the ground as long as the vehicle is at rest. In such a condition, the vehicle is supported on wheels 6. The vehicle V is driven by means of a known linear motor, consisting of the superconducting coils 2 and 2' mounted on the vehicle and the conductor coils 4 and 4' installed on the track for propulsion and guidance. Thus the superconducting coils 2 and 2' move along the conductor coils 3 and 3' continuously set at definite intervals along the track 5 in the direction of travel of the vehicle, and thereby a current is induced in the conductor coils 3 and 3' by the superconducting coils 2 and 2'. The induced current grows with an increase in the vehicle speed and at a certain speed, say, about 200 Km/h, the conductor coils are nearly saturated. Said current is held at the same level as long as the vehicle runs at this speed or faster. Then in the conductor coils 3 and 3' there develops a linkage magnetic flux as depicted in FIG. 2(b) positionally corresponding to said coils, while at the same time a voltage e for levitation of the vehicle is induced as depicted in FIG. 2(c) positionally corresponding similarly, whereupon a current as depicted in FIG. 2(d) flows.
When the current in the superconducting coil 2 flows as indicated in FIG. 2(e), the current induced in the conductor coil 3 by the above-mentioned current will flow as indicated in FIG. 2(e). In consequence, according to Fleming's left hand law, the levitating force F will be equal to B.times.i, where B is the density of the magnetic flux generated by the superconducting coils 2 and 2' and i is the current flowing in the conductor coils 3 and 3'. Thus the vehicle V is levitated by the repulsing force acting between the currents induced in the conductor coils 3 and 3' and in the superconducting coils 2 and 2'.
The guidance and propulsion of the vehicle V are accomplished as follows.
The cross-sectional areas of the conductor coils 4 and 4' are made equal and the spacing between the superconducting coils and the conductor coils 2 and 4 and 2' and 4' are also made equal. As indicated in FIG. 4, the conductor coils 4 and 4' are null-flux connected. If linkage magnetic fluxes .phi.g and .phi.g' develop in the respective conductor coils 4 and 4' due to the opposed superconducting coils 2 and 2' while the vehicle is running, then if there is no displacement of the vehicle in either direction, .phi.g=.phi.g' and accordingly the developed linkage magnetic flux for a set of coils will be .phi.g-.phi.g'=0 and no current will be induced, which means no generation of a guiding force occurs. In contrast, if there is any displacement of the vehicle in either direction, .phi.g&gt;.phi.g' (the vehicle moves rightward) or .phi.g&lt;.phi.g' (the vehicle moves leftward) and then the developed linkage magnetic flux for a set of coils will be .phi.g-.phi.g'=.+-..DELTA..phi.g', and then the current flows in the conductor coils 4 and 4' as indicated by the solid arrow in FIG. 4, and a guiding force proportional to this displacement in a direction nullifying said displacement will be generated from repulsion between the left side superconducting coil 2 and conductor coil 4 and attraction between the right side superconducting coil 2' and conductor coil 4'.
Meanwhile, as indicated in FIG. 4 a power source 41 of three or poly phases for propulsion of the vehicle is connected to the conductor coils 4 and 4' for both propulsion and guidance of the vehicle. Since said power source provides a current in the flow direction indicated by the dotted arrow to the conductors 4 and 4' for both propulsion and guidance, a propelling force to move the vehicle V occurs in accordance with Fleming's left hand law.
In this system powering, coasting, braking and stopping of the vehicle is effected by controlling the current supplied from a power source 41 to the conductor coils 4 and 4' for both propulsion and guidance.
When the vehicle begins to move driven by the propulsion force generated by the conductor coils 4 and 4' for both propulsion and guidance, levitating force is generated through interaction between the superconducting coils 2 and 2' and the conductor ooils 3 and 3', while a guiding force is generated through interaction between the superconducting coils 2 and 2' and the conductor coils 4 and 4'. After the vehicle attains a certain level of speed, the vehicle is levitated and guided while a constant state of levitation is maintained, thereby allowing the wheels 6 to be raised. When the speed becomes lower than said certain level, the levitation force drops and is gradually lost, and the vehicle must be supported on the ground track 5 by means of the auxiliary support such as the wheels 6. In FIG. 1, a mechanical guide wheel 7 is rotatably mounted on the end of each of shafts 71 the other end of which is fixed to the vehicle, said wheels rolling along the respective sides of the track 5 and serving to guide the vehicle. Shafts 61 are fixed to the truck 1 at one end and have the respective wheels 6 rotatably mounted on the other ends thereof.
In this inductive repulsion type magnetically levitated railway in which the conductor coils 3 and 3' for levitation on the ground are located on the track 5 in a horizontal position and the superconducting coils 2 and 2' on the vehicle are vertically mounted on the sides of the truck facing in the lateral direction, a large induced current must be passed through the conductor coils 3 and 3' for levitation in order to generate an effective levitating force between the superconducting coils and the conductor coils. Thus Joule losses suffered in the conductor coils 3 and 3' grow large because of the large current induced in the conductor coils 3 and 3' and there is a limit to how much the running resistance can be decreased.
In addition, the conductor coils 4 and 4' on the sides of the track and which serve for both propulsion and guidance of the vehicle have a power source for propulsion connected thereto and these coils have a high voltage impressed thereon. The null-flux cable 14 connecting the right and left conductor coils 4 and 4' must therefore be designed such as to be able to withstand a high voltage, which results in complexity of structure and high cost of the cable. In order to avoid imposing such a high voltage on the null-flux cable 14, it is possible to provide separate coils for propulsion and for guidance, but this will result in an increased number of coils.